Electrical contact



Oct. 23,1951 L. 'r. RICHARDSON EI'AL 2,572,652

' ELECTRICAL CONTACT Filed July 12, 1945 MIXTURE OF INDIUM Oxujz AND AMETALLIC SALT.

METAL. OF 6000 ELECTRICAL. CONDUCTIVITY.

wxa y mwlw Mme Patented Oct. 23, 1951 ELECTRICAL CONTACT Linwood T.Richardson, Wauwatosa, and Merle R. Swinehart, Milwaukee, Wis.,assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation ofDelaware Application July 12, 1945, Serial No. 604,600

4 Claims.

This invention relates trical contacts.

An object of the invention is to provide for use of indium oxide in thecomposition of contact tips of the general character herein referred to,

to improvements in elecwith unexpectedly improved results of thecharacter hereinafter specified.

Another object is to provide for use of indium oxide in a contactcomposition, either with or without the addition of a suitablerelatively small proportion of a metallic salt.

Another object is to provide for. attainment of certain desirable andimportant results by combining a metallic salt with the indium oxide.

Other objects and advantages of the invention will hereinafter appear.

The single figure of the accompanying drawing is a fragmentary sectionalview, highly magnified, of an electrical contact embodying ourinvention.

In producing an electrical contact of the aforementioned charactercomposed essentially of silver powder and indium oxide, we prefer toemploy precipitated silver powder (which is characterized by a fibroustexture, extreme whiteness, and an unusual ability to cold weld underpressure to a tough solid of considerable tensile strength) and acommercial form of indium oxide which may initially be of such finenessas to pass through a 325 mesh screen. The indium oxide is densified bypressing, or by pressing and heat sintering operations, and thereafterground in such a manner that at least fifty per cent of the powder whichpasses through a 100 mesh screen will be retained upon a 300 meshscreen. The pressure employed for densifying the indium oxide (InzOs)may be varied throughout a wide range; as for example, from 40,000pounds per square inch to 100,000 pounds or more per square The additionof one or another of such metallic salts (or combinations of two or morethereof) improves to a marked degree the anti-welding or non-stickingcharacteristics of the particular contact, and thus substantiallyincreases the range of currents which such contacts will make and break.Such a metallic salt or salts when thus employed likewise insures a moreeven wear of the contacts, and consequently substantially increases thelength of useful life of the latter.

The aforedescribed granular powder composed of indium oxide (either withor without the aforesilver powder, and such mixture of powders is inch.In the example hereinafter given a moldthen cold molded at a pressure ofabout 40,000 pounds per square inch to provide disk-shaped preforms ofapproximately three-fourths of an inch in diameter. Thereafter saidpreforms are subjected to a temperature of about 1600 degrees F. forabout twenty minutes. After such heat treatment said preforms aresubjected to a molding pressure of about 100,000 pounds per square inchto produce the finished contacts.

We have found that a contact consisting of per cent by weight of silverpowder, of the character aforedescribed, and 15 per cent by weight ofindium oxide, when subjected to the aforedescribed method of treatment,had non-sticking and non-transferring characteristics substantially likeor equivalent to those of a silver-cadmium oxide contact similarlyproduced. However, the contact resistance of the silver-indium oxidecontact of the present invention was substantially lower than that ofthe contact having similar proportions of silver and cadmium oxide.Moreover, we have found that a set of contacts produced in the manneraforedescribed and consisting of only silver powder and as little as 7.5per cent by weight of indium oxide will not transfer to any appreciableextent when operated tomake and break a 200 ampere, 28 volt directcurrent resistance load. In contrast, we have found by experiment thatat least 10 per cent by weight of cadmium oxide is-required, in theaforementioned silver-cadmium oxide contacts of the Swinehart Patent No.2,425,052, to provide for attainment of a substantially similar result.

Although we have herein specified examples involving use of 7 .5 percent and 15 per cent, by

scale for purposes of illustration, of an electrical contact embodyingour invention. In this-sectional view, the numeral 6 designates the baseor matrix material, which consists of a metal of good electricalconductivity, such asv precipi tated silver powder; and the numeral?designates particles or granules of a mixture of indium oxide and ametallic salt (of the group consist:-

ing of silver iodide, silver bromide, silver chloride,.

cadmium chloride and cadmium sulphate). The materials in powder form aretreated in the manner 'afbredescribed to produce the final article.

One example of contacts produced in accordance with our invention i'sasfollowsi Contacts three-fourths of an inch in diameter, formed underheavy pressure and heat s-intered, may be composed of an intimatemixtureof 8-2 per cent by weight of precipitated silver powder-i 14.5 per centof indium oxide prepared as aforedescribed; and' 3.5 per cent of silveriodide.

Such contacts will have substantiallythe same utility for use in thecontrol of alternating current circuits involving relatively hi hamperage, as would be provided by contacts of otherwise similarcomposition but having a corresponding percentage of cadmium oxidesubstituted for the indium oxide above-mentioned. However, asaforeindicated, when said contacts involving use of indium oxide are tobe used in direct current circuits they afford certain' very definiteadvantages, in respect of minimizing the contact resistance of thecontacts.

' The aforementioned beneficial action of the added metallic salt (ofthe groupaforementioned) in preventing sticking of the contacts and intheir ability to extinguish very heavy alternating current arcs, ispresent in respect of contacts of the character herein contemplatedinvolving use of silver powder and indium oxide, it appearing:

1. That the volatilized metallic salt produces an ionized atmosphere atthe operating surface of at least one of the cooperating contacts of apair. Such ionized atmosphere effects spreading of the arc at the arcfeet, which inh rently results in lower current density and reducedheating of the contact surface or surfaces by the arc; Such decreasedheating by the arc involves a reduction of pin-pointformations of moltensilver upon the contact or contacts, which pin-point formations, ifnumerous; might cause welding or sticking of the cooperating contactsurfaces upon subsequent operations.

2. That the condensation of the metallic salt or salts as a thin film unon the surface or surfaces acts to prevent bonding or sticking of thesilvers of the cooperating contact faces in subseouent operations.

, 3. That the aforementioned. silver halides (silver iodide, bromide orchloride), in addition tacts when in operation, likewise act to preventthe contact resistance from increasing throughout the life of thecontact, and in most cases actually result in a decrease in contactresistance. It is thought that such reduction in contact resistance maybe due to the presence of additional silver upon the surface of thecontact or contacts as a result of decomposition of the particularmetallic salt employed, and also to the action of such metallic salt inweakening the. exposed indium oxide particles so that they may be morereadily broken up by mechanical and arcing action as aforedescribed.

While we have herein disclosed our invention fibrous texture, and from:about seven and one 2. A pressure molded and heat sintered powdercomposition electrical contact consisting of a mixture of abouteighty-two per cent by weight of fine silver, aboutfourteen and onevhaifper cent of indium oxide, and about three and one-r half per cent of ametallic salt of the groupconsisting of silver iodide, silver bromide,siiver chloride, cadmium chloride and cadmium sulphate, said indiumoxide and said metallic salt being in the form of a compositiondensified by heat sintering, at least one-half of saidlast mentionedcomposition being in the form of par ticles larger than those which willpass through a 300 mesh screen and small enough to pass through a 100mesh screen, said particles being dispersed throughout the mass of finesilver which serves as a matrix therefor.

3; A pressure molded silver base powder composition electrical contactconsisting of fine silver of fibrous texture, indium oxide, and a silverhalide, said indium oxide being present in an amount of not less thanseven and one-half" per cent nor more than twenty-one and one-fourth percent by weight of the entire mass, and said silver halide being presentin an amount. of not less than one-half of one per cent nor more thanthree and three-fourths .per cent by weight of the entire mass.

4. A pressure molded and heat sintered silver base powder compositionelectrical contact, said contact consisting of approximately eighty-twoper cent by weight of fine silver of fibrous. texture, approximatelyfourteen and one-half per cent by weight of indium oxide,. andapproximately three and one-half per cent by weightof silver iodide,said indium oxide and silver iodide being jointly in the form of dense,heat sintered' particles all of which will pass through a 100" meshscreen,

to preventing sticking of the cooperating conthe majority of. which D wbe retained upon a 300 mesh screen, said particles being dispersedthroughout the mass of fine silver which serves as a matrix therefor,and said contact having non-sticking and low contact resistancecharacteristics.

LINWOOD T. RICHARDSON. MERLE R. SWINEHART.

REFERENCES CITED The following references are of record in the 10 NumberName Date Zickrick Oct. 13, 1936 15 Number Name Date 2,157,933 Hensel eta1. May 9, 1939 2,200,854 Ruben May 14, 1940 2,200,855 Ruben May 14,1940 2,288,122 Cox June 30, 1942 2,307,668 Cox Jan. 5, 1943 2,425,052Swinehart Aug. 5, 1947 OTHER REFERENCES LeBlanc et a1.: ElectronConductivity of solid oxides of varying balances, Chemical Abstract,v01. 26, page 12.

1. A PRSSURE MOLDED AND HEAT SINTERED POWDER COMPOSITION ELECTRICALCONTACT CONSISTING OF A MIXTURE OF A QUANTITY OF PRECIPITATED SILVER OFFIBROUS TEXTURE, AND FROM ABOUT SEVEN AND ONEHALF PER CENT TO FIFTEENPER CENT B WEIGHT OF THE ENTIRE MASS OF INDIUM OXIDE, SAID INDIUM OXIDEBEING IN THE FORM OF PARTICLES ALL OF WHICH WILL PASS THROUGH A 100 MESHSCREEN AND THE MAJOR PORTION OF SAID PARTICLES BEING OF A SIZE GREATERTHAN THAT WHICH WILL PASS THROUGH A 300 MESH SCREEN, SAID PARTICLES OFINIDIUM OXIDE BEING DISPERSED THROUGHOUT THE MASS OF SILVER WHICH SERVESAS A MATRIX THEREFOR.